What topics do you discuss with a mentor in an organization?

I am have a recurring meeting with a higher level exec in my company. We have a good relationship but during these meetings I am finding it difficult to come up with meaningful topics to talk about. I obviously value his time and don't want to waste his time, at the same time want to make sure I don't lose his ear as well.

Hoping I can get some suggestions on topics to talk about and in general advice on how best to handle this.